The response of a subject's circulation system to a subject's posture change may depend upon characteristics of the blood such as its viscosity, characteristics of the circulation system such as its resistance and how the autonomous nervous system responds to maintain homeostasis.
Blood perfusion at a periphery may, for example, be dependent upon one or a combination of the following factors:—                1. vascular disease such as for example Raynaud's disease        2. genetic problems such as for example scleroderma        3. an abnormal vaso-constriction or vaso-dilation response from the autonomous nervous system instigated by for example diabetic neuropathy or alcoholism        4. drug treatments such as for example Beta blockers        5. auto-immune diseases such as for example Lupus        
It will therefore be appreciated that there may be many reasons why a subject's circulatory system response to a postural change may be “abnormal”. Different pathologies may have the same or different effects on circulation.
It would be desirable to provide an interim clinical indicator that characterizes a response of the circulation system to a series of postural changes and provides a clinician with information which in combination with other information and the clinician's skill and knowledge may be used to assess whether or not pathology may be present. The medical practitioner can then, using his own medical knowledge, conduct independent investigations before identifying any pathology.